1. Field of the Invention
The present invention relates to a semiconductor device, and particularly, to the technology field of a semiconductor device for ESD protection.
2. Description of the Related Art
A zener diode is a device to protect electrical equipment or the like from an electrostatic discharge (ESD). The zener diode undergoes, when a high voltage pulse such as a surge is applied between the anode and the cathode of the diode, a zener breakdown or an avalanche breakdown. This phenomenon flows a current between the anode and the cathode, thereby suppressing the voltage increase. The zener diode thus functions as the ESD protection device. For a high-frequency and high-voltage pulse, however, the zener diode needs a large junction area to ensure a sufficient capacitance. This is an obstacle to a more compact zener diode.
As an alternative ESD protection device that can provide a smaller junction area and thus a more compact device size than the zener diode, a bi-directional two-terminal thyristor is known. The thyristor is disclosed in, for example, JPH 8-316456. The bi-directional two-terminal thyristor is formed to have a vertical shape on the semiconductor substrate such as a silicon substrate. The semiconductor substrate should thus have an N-type semiconductor region and a P-type semiconductor region formed on the respective sides thereof. Unfortunately, it requires a complicated manufacturing process to form the n and P-type semiconductor regions on the respective sides of the semiconductor substrate. This requires significant time and effort, resulting in a high cost. In addition, it is difficult to provide a process such as grinding to the substrate sides on which the n and P-type semiconductor regions are formed. This prevents the thyristor from being more compact.